Simvastatin treatment attenuates increased respiratory variability and apnea/hypopnea index in rats with chronic heart failure

Abstract

Cheyne-Stokes respiration and cardiac arrhythmias are associated with increased morbidity and mortality in patients with chronic heart failure (CHF). Enhanced carotid body chemoreflex (CBC) sensitivity is associated with these abnormalities in CHF. Reduced carotid body (CB) nitric oxide and nitric oxide synthase (NOS) levels play an important role in the enhanced CBC. In other disease models, Simvastatin (statin) treatment increases endothelial NOS, in part, by increasing Krüppel-like Factor 2 expression. We hypothesized that statin treatment would ameliorate enhanced CBC sensitivity as well as increased respiratory variability, apnea/hypopnea index, and arrhythmia index, in a rodent model of CHF. Resting breathing pattern, cardiac rhythm, and the ventilatory and CB chemoreceptor afferent responses to hypoxia were assessed in rats with CHF induced by coronary ligation. CHF was associated with enhanced ventilatory and CB afferent responses to hypoxia as well as increased respiratory variability, apnea/hypopnea index, and arrhythmia index. Statin treatment prevented the increases in CBC sensitivity and the concomitant increases in respiratory variability, apnea/hypopnea index, and arrhythmia index. Krüppel-like Factor 2 and endothelial NOS protein were decreased in the CB and nucleus tractus solitarii of CHF animals, and statin treatment increased the expression of these proteins. Our findings demonstrate that the increased CBC sensitivity, respiratory instability, and cardiac arrhythmias observed in CHF are ameliorated by statin treatment and suggest that statins may be an effective treatment for Cheyne-Stokes respiration and arrhythmias in patient populations with high chemoreflex sensitivity.

Keywords: Cheyne–Stokes Respiration; carotid body; simvastatin; systolic heart failure.

Figure 1. Simvastatin reduced respiratory variability in CHF

(A) Representative plethysmographic records taken during resting breathing in sham (upper trace), CHF vehicle (middle trace), and CHF statin (lower trace) rats. (B) Representative Poincare plots calculated over the course of 300 consecutive breaths in the animals shown in panel A. (C) Summary data for analysis of short term (SD1) and long term (SD2) respiratory variability in each group of animals (n = 6 per group). (D) Apnea/hypopnea index (AHI) was significantly increased in CHF vehicle animals and prevented by statin treatment. * p < 0.05 vs. CHF vehicle.

Figure 2. Simvastatin reduced arrhythmia incidence in CHF

(A) Representative tracings of heart rate taken during resting measurement in sham vehicle, CHF vehicle, and CHF statin animals. (B) An expanded scale of the arterial pressure tracings taken during the time periods indicated by the dashed lines in panel A. This tracing shows the arrhythmic episodes indicated by the deflections in the heart rate tracing shown in panel A. (C) Arrhythmia incidence was increased in CHF and this effect was attenuated by Simvastatin treatment (A & C). n=4-6 rats in each group.

Figure 3. Simvastatin normalized the chemoreflex ventilatory response to hypoxia in CHF

(A) Representative plethysmographic records showing the ventilatory response to isocapnic hypoxia in CHF animals with and without statin treatment. (B) Mean data for the ventilatory responses to isocapnic hypoxia showing that the carotid body chemoreflex was enhanced in CHF and that statin treatment prevented this effect. * p < 0.05 vs. CHF statin, # p < 0.05 vs. sham vehicle.

Figure 4. Simvastatin reduced CB chemoreceptor afferent nerve activity in CHF

Summary data showing the effect of statin treatment on the CB chemosensory afferent discharge to hypoxia (n=4 per group). CHF rats displayed enhanced CB chemosensory responses to acute hypoxia (F_iO₂ 2-10%) compared to the responses observed in sham rats. Note that statin treatment restored normal CB afferent discharge in CHF statin rats. * p < 0.05 vs. sham vehicle, # p < 0.05 vs. CHF statin.

Figure 5. Simvastatin normalized KLF2, eNOS, and AT1R protein expression in the CB and NTS in CHF

Representative western blots (upper panels) and mean data (lower panels) showing (A) KLF2, (B) eNOS and (C) AT1R expression in Sham, CHF and statin treated groups. * p < 0.05 vs. sham vehicle, # p < 0.05 vs. CHF statin, n=4-6 rats in each group.

Figure 6. Immunolocalization of KLF2 in the CB of CHF rats

Representative image from a CB from a Sham vehicle rat, a CHF vehicle and a CHF statin rat. KLF2 staining was localized to TH positive glomus cells (arrow) and blood vessels (asterisk). Apparent decreases in KLF2 immunostaining were evident in the CBs from CHF rats. Note that CHF rats treated with statin displayed an increased KLF2 staining in the CB. Scale bar = 100 μm. Negative control was performed by omission of the primary antibody.